A354714 Nonprime numbers k such that the number of divisors of k divides k+1.

1, 15, 27, 35, 39, 51, 55, 87, 91, 95, 111, 115, 119, 123, 135, 143, 155, 159, 183, 187, 203, 215, 219, 231, 235, 245, 247, 255, 259, 267, 275, 287, 291, 295, 299, 303, 319, 323, 327, 335, 339, 343, 351, 355, 371, 375, 391, 395, 399, 403, 407, 411, 415, 425, 427, 447, 451, 455, 471, 511, 515

Offset: 1

Author

Max Alekseyev, Jun 03 2022

Keywords

• nonn

Comments

Nonprime numbers k such that k == -1 (mod A000005(k)).

Crossrefs

Nonprime terms of A272872.

Cf. A000005, A033950, A354711, A354712, A354715, A354716.

Programs

Mathematica

Select[Range[500], ! PrimeQ[#] && Divisible[# + 1, DivisorSigma[0, #]] &] (* Amiram Eldar, Jun 03 2022 *)